Root-lesion nematodes, Pratylenchus spp., are serious pathogens of potato plants worldwide. Several management practices can control Pratylenchus spp.; however, they all have shown some limitations. Therefore, environmentally-safe, low-cost, and effective control strategies are needed as possible alternative to currently used strategies. This thesis was designed to assess if liquid hog manure (LHM) holds such potential. The objectives of this thesis were to determine: (i) the prevalence and identity of species of Pratylenchus spp. in Manitoba potato fields, (ii) if short-chain volatile fatty acids (VFA) in LHM are the constituents responsible for the manure’s toxicity to Pratylenchus spp. using solution exposure experiments (iii) the effectiveness of LHM in killing Pratylenchus spp. in soil, and (iv) the impact of LHM on nematode communities. Pratylenchus spp. were detected in 39% of 31 potato fields surveyed in Manitoba with population densities ranging, for positive fields, from 45 to 631 nematodes kg-1 fresh soil. Morphometrics of female nematodes and molecular diagnosis (using species-specific PCR primers) showed that the species of Pratylenchus present in the potato fields to be P. neglectus. Potato, cv. Russet Burbank, showed to be a poor host to two populations of Pratylenchus spp. from Manitoba potato fields. Accordingly, P. neglectus does not seem to be a limitation to potato production in Manitoba; thus, P. penetrans, the most widely spread and damaging species to potato was used in the successive studies of assessing the use of LHM to control Pratylenchus spp. in potato fields. VFA (acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, and n-caproic acids) accounted for the majority of the lethal effect of LHM to P. penetrans under acidic conditions. VFA in LHM killed Pratylenchus spp. in soil and acidification seemed to enhance its ability when VFA concentration in the manure is low. LHM did not act as a soil fumigant eliminating soil trophic interactions but increased bottom-up food web interactions. VFA in LHM persisted in the soil for four days with biological degradation being their mode of loss. In conclusion, LHM is potentially an effective and low-cost strategy to control Pratylenchus spp. and its efficacy can be improved by acidification.

Root-lesion nematodes, Pratylenchus spp., are serious pathogens of potato plants worldwide. Several management practices can control Pratylenchus spp.; however, they all have shown some limitations. Therefore, environmentally-safe, low-cost, and effective control strategies are needed as possible alternative to currently used strategies. This thesis was designed to assess if liquid hog manure (LHM) holds such potential. The objectives of this thesis were to determine: (i) the prevalence and identity of species of Pratylenchus spp. in Manitoba potato fields, (ii) if short-chain volatile fatty acids (VFA) in LHM are the constituents responsible for the manure’s toxicity to Pratylenchus spp. using solution exposure experiments (iii) the effectiveness of LHM in killing Pratylenchus spp. in soil, and (iv) the impact of LHM on nematode communities. Pratylenchus spp. were detected in 39% of 31 potato fields surveyed in Manitoba with population densities ranging, for positive fields, from 45 to 631 nematodes kg-1 fresh soil. Morphometrics of female nematodes and molecular diagnosis (using species-specific PCR primers) showed that the species of Pratylenchus present in the potato fields to be P. neglectus. Potato, cv. Russet Burbank, showed to be a poor host to two populations of Pratylenchus spp. from Manitoba potato fields. Accordingly, P. neglectus does not seem to be a limitation to potato production in Manitoba; thus, P. penetrans, the most widely spread and damaging species to potato was used in the successive studies of assessing the use of LHM to control Pratylenchus spp. in potato fields. VFA (acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, and n-caproic acids) accounted for the majority of the lethal effect of LHM to P. penetrans under acidic conditions. VFA in LHM killed Pratylenchus spp. in soil and acidification seemed to enhance its ability when VFA concentration in the manure is low. LHM did not act as a soil fumigant eliminating soil trophic interactions but increased bottom-up food web interactions. VFA in LHM persisted in the soil for four days with biological degradation being their mode of loss. In conclusion, LHM is potentially an effective and low-cost strategy to control Pratylenchus spp. and its efficacy can be improved by acidification.

Att uppnå de globala målen är av vikt för en hållbar utveckling. Odugliga jordbruksmetoder utgör en stor del av de klimathot som planeten i stunden utsätts för. Det är av intresse att undersöka vilka hållbarhetsvinster som kan erhållas vid regenerativ bomull samt definiera begreppet. Regenerativ bomull definieras utifrån det faktum att bomullen är odlad i enlighet med regenerativa jordbruksmetoder. De regenerativa jordbruksmetoderna är således både en inställning samt praxis. Metodens fokus är att bevara samt förbättra planetens jordhälsa. En frisk jord bidrar till att biologisk mångfald, kolinlagring samt fotosyntesens fortgång ökar. Konventionella metoder vid bomullsproduktionen bidrar till att jorden utarmas vilket leder till en försvagad biologisk mångfald och drastiska klimatförändringar. I den konventionella andelen bomull ingår även BCI-certifierad bomull vilken anses som något bättre i jämförelse då den innefattar principer som skall gynna den hållbara utvecklingen. Det är dock enbart initiativ till förbättring som uppmanas och inga faktiska krav ställs. Ekologiskt odlad bomull genomförs enligt den odlingsmetod som ställer mer miljövänliga krav men den globala andelen utgörs enbart av 1%. För att sammanställa litteraturstudien har en bred informationsinsamling genomförts innehållande bland annat bomull, certifieringar, jordbruk, regenerativa jordbruksmetoder samt klimatpåverkan vid dåligt utfört jordbruk. Studien tar hänsyn till ekologiska, sociala samt ekonomiska hållbarhetsaspekter och resultatet återspeglas i en sammanställd tabell där de olika jordbruksmetodernas skillnader ställs mot varandra. Slutsatsen belyser att det finns svårigheter med att få jordbrukare att konvertera till de regenerativa jordbruksmetoderna. Svårigheterna ligger bland annat i de likheter på krav som ställs vid omställning till ekologiskt jordbruk. Då denna ej har uppgått till en procentuellt större andel globalt blir det svårt att inom tidsramen för Agenda 2030 få regenerativa odlingsmetoder att lyfta. Däremot är den regenerativa odlingsmetodens krav essentiella och tillsammans utgör de en del av lösningen på världens klimatproblem. Det regenerativa jordbruket har potential att bidra till hållbarhetsvinster genom att bland annat öka kolinlagringen i jorden och motverka klimathoten. En omställning i jordbrukspraxis som gynnar hållbar utveckling är av yttersta vikt. / Poor farming practices have a major impact on the environment. The current cotton production is environmentally unsustainable and to achieve the global goals, it is necessary to call for action. Included in the conventional grown cotton is BCI-cotton, these methods aim for a more environmentally friendly approach for farmers but does not include any requirements. Organically grown cotton sets certain requirements, but it does not exceed 1% globally. It is therefore of interest to investigate if regenerative cotton can obtain any sustainable profits. It is also of interest to define the concept of regenerative cotton. It is concluded that regenerative cotton is rather regenerative agriculture, and this is both an attitude and a suite of practices. The practical methods are based on the same biological components that create and maintain life on the planet. The utmost importance lies in the health of the soil. Healthy soil contributes to positive aspects including increased photosynthesis, storing carbon, and biodiversity. The literature study has been conducted to assemble information about cotton, organic certifications, regenerative farming practices, and environmental losses due to poor agriculture. The result is presented as a table which includes a comparison between the different agricultural practices and both ecological, social, and economic aspects are considered to the sustainable development. The major difficulties of converting to regenerative cotton lies in the similarities to convert to organic. It will be challenging for farmers due to the lack of knowledge for these new method’s positive aspects. It will be difficult to implement a major adjustment required within the timeframe for the 2030´s Agenda, but a shift towards sustainable development is necessary. The combined factors and requirements for regenerative agriculture are one solution to the climate change.

Thesis (Ph. D. Agriculture (Plant Production)) -- University of Limpopo, 2021 / Plant-parasitic nematodes inflict economic damages on vegetable and field crops due to a lack of suitable crop protection chemicals and integrated crop management practices. Toxic synthetic chemical nematicides were withdrawn from the agro-chemical markets in 2005 due to their damage to the environment and humans. As such, there is continuous need to develop integrated nematode management strategies that are economic, environment friendly yet capable of effectively controlling the pest to alleviate crop loss and food insecurity. Root-knot (Meloidogyne species) nematodes are a major yield- and quality-reducing pest in most potato (Solanum tuberosum L.) producing regions in South Africa. However, little is known about the different plant-parasitic nematode species that are associated with potato in some Provinces. The sustainable production of crops in the absence of nematode resistant genotypes depends on the availability of nematode resistant crops in crop rotation systems. However, the effectiveness of these nematode resistance crops in managing root-knot nematodes in potato-based cropping systems has not been investigated in South Africa. The aim of the study was the development of sustainable cropping sequences for management of population densities of Meloidogyne species in potato production using crops with different mechanisms of nematode resistance. Two main objectives were investigated, but the second objective was sub-divided into three. The objectives of the study were to investigate (1) whether the diversity and abundance of plant-parasitic nematodes associated with potato in Limpopo Province, would be different to those in other potato-producing regions of South Africa, (2) whether (a) monoculturing potato would have any effects on population densities of Meloidogyne species, plant growth and soil health, (b) sequencing potato with a post-infectional nematode resistant crop like Cucumis africanus would have any effects on population densities of Meloidogyne species, plant growth and soil health and (c) sequencing potato with a pre-infectional nematode resistant crop such as sweet stem sorghum would have any effects on population densities of Meloidogyne species, plant growth and soil health. Ten known nematode genera, namely, Scutellonema, Helicotylenchus, Telotylenchus, Rotylenchulus, Paratylenchus, Tylenchorhynchus, Criconema, Nanidorus, Meloidogyne and Pratylenchus species were present in potato production fields in Limpopo Province, South Africa. The study was conducted on 30 farms, located in Mopani, Sekhukhune, Capricorn, and Waterberg districts by randomly collecting 10 core soil samples per hectare in a zigzag-sampling pattern. A total of eight nematode genera except two (Meloidogyne and Pratylenchus species) were recorded for the first time in potato fields in Limpopo Province. Additionally, the sampled districts were predominated by different nematode species. The Meloidogyne species were the most prevalent nematodes associated with potato crops followed by Helicotylenchus and Scutellonema species. In contrast, the Tylenchorhynchus and Nanidorus species were the least prevalent parasitic nematodes in potato production fields in the Limpopo Province. To achieve Objective 2, two field experiments were conducted at the University of Limpopo (UL) and the Agricultural Research Council-Vegetable and Ornamental Plants (ARC-VOP). In Sequence 1, the treatments (sorghum cv. ʹNdendaneʹ, potato cv. ′Mondial G3′, Cucumis africanus and potato (cv. ′Mondial G3′)-(Velum) were laid out in a randomised complete block design. In Sequence 2, potato (cv. ′Mondial G3′) was cultivated on all plots as the successor main crop. In Sequence 3, the treatments were laid out as in Sequence 1, whereas in Sequence 4 sole potato crop was cultivated as in Sequence 2. Therefore, four cropping sequences namely, sorghum-potato, potato monoculture, C. africanus–potato and potato-(Velum)-potato (control) were investigated simultaneously.Generally, post-infectional resistant C. africanus-potato was more effective than pre-infectional nematode resistant sorghum-potato or potato monoculture cropping sequences in reducing the population densities of Meloidogyne species in the soil. This has led to reduced damage to subsequent potato crop providing higher tuber yield, increased shoot mass and nutrients elements accumulation in potato leaf tissues at both sites. The high soil organic carbon content, microbial diversity and enzyme activity observed in C. africanus-potato and sorghum-potato showed that these two cropping sequences enhanced soil health better than the monoculture production system of potato with or without Velum application. The different indices (maturity index, channel index, enrichment index and structure index) collectively demonstrated that the soil was highly disturbed with bacteria dominated decomposition pathways. The nematode faunal profile showed that sorghum-potato was the only cropping sequence that improved soil structure as exhibited by high structure index. Therefore, the inclusion of nematode resistant sweet stem sorghum in potato-based cropping system promoted soil health better than the other cropping sequences. In conclusion, C. africanus-potato sequence could be used to effectively manage root-knot nematode population densities, whereas sorghum-potato sequence could be considered where the aim is to improve soil health. / National Research Foundation(NRF) Green Biotechnologies Research Centre of Excellence(GBRCE) Agricultural Research Council-Vegetable and Ornamental Plants(ARC-VOP)

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Thesis (M.Sc. Agriculture (Soil Science)) -- University of Limpopo, 2022 / Soil health support crop production and answer to its sustainability and renewability. This study involved the use of under explored legumes in South Africa, Limpopo under maizelegume intercropping systems as a strategy to mitigate soil quality deterioration. The study was conducted at University of Limpopo (Syferkuil) and University of Venda (UNIVEN) Experimental farms during 2020/2021. A split plot experiment, with the main factor comprised of water regimes (irrigation and rainfed) and second main factor included cropping systems (Intercropping and monocropping). Five treatments comprised of 3 monocrops (Maize, Chickpea, and Mungbean) and 2 intercrops (maize-chickpea and maize-mungbean) replicated three times. Data collected from the soil before planting and after maturity were pH, Electrical conductivity (EC), particle size, bulk density, aggregate stability, organic matter (OM), organic carbon (OC), phosphorus (P), ammonium (NH4-N), nitrate (NO3—N), soil active carbon (SAC), and potentially mineralizable nitrogen (PMN). Plant parameters collected during vegetative and flowering stage included plant height, chlorophyll content, plant vigour, and leaf area index. All data was subjected to descriptive statistics and analysis of variance using GenStat software. Significant effect (p<0.05) was observed between treatments on soil pH (KCl), OM, organic carbon (OC), and ammonium (NH4) at Syferkuil Farm. Also, interaction between water regimes and cropping systems affected NH4 and pH (KCl). Cropping systems had significant effect (p<0.01) on pH (H2O), OM, OC, P, NH4, and NO3 at UNIVEN. Interaction between water regimes and cropping systems affected (p<0.01) pH (H2O), P but no significant effect was observed on OC, NH4, and NO3. Cropping systems and interaction at both locations did not affect particle size, bulk density, aggregate stability, EC, SAC, and PMN. Pure stands of maize and legumes had greater plant height, plant vigour, and chlorophyll content whereas intercrops had greater LAI. The results at both locations revealed that legume intercropping systems improved soil health variables without posing negative feedbacks and hence can be used to boost soil functioning. Keywords: Soil health, maize-legume intercropping, soil quality / National Research Foundation (NRF)

Soils provide many essential functions that support the world. With a decline in soil health, these functions also decrease in efficiency, and can threaten the health of billions of people around the world. Typically, soil health tests do not use biological indicators, however microbes drive and perform vital functions to increase soil health. One way to increase soil health is through the use of cover crops to reduce soil erosion during fallow periods, increasing soil organic matter, as well as collecting nutrients from soil into their biomass. These cover crops are then terminated through various methods such as herbicides, disk tillage, or no tillage. The termination method can have an impact on soil health, by chemically affecting soil microbes with herbicides, disturbing soil, microbial communities, and fungi with tillage, or creating residue barriers on the surface of soil such as with using roller crimping (no tillage). Fertilization can also affect soil health, controlling rates of nutrient turnover and decomposition through the needs of microbes for carbon and nitrogen. This study quantifies the effects of four termination methods and four fertilization treatments on soil biological indicators during one growing season of sweet corn. Plots that were not tilled and terminated using roller crimping showed highest rates of decomposition, as well as increased labile carbon pools to feed microbes slowly throughout the growing season. Microbial activity was also observed to respond to fertilization, as patterns in activity spiked directly after fertilization. This study informs agricultural land management by the usage of biological indicators to further support the use of cover crops to increase soil health along with using no-till termination methods. Root biomass contributions toward soil health was also investigated, and how they may be affected by tillage.

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No description available.